The present application relates to systems, devices and methods for substrate inspection using charged particle beams.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Defect inspection of semiconductor wafers and masks for IC manufacturing is an accepted production process for yield enhancement. The information obtained from a wafer defect inspection tool can be used, for example, to flag defective wafers for reprocessing or discarding, or to correct wafer processing parameters.
Various charged particle beam technologies can be suitable for wafer inspection, including electron beam, focused ion beam, and masked ion beam systems. Inspection uses beam powers low enough not to significantly affect the wafer surface (i.e., low enough not to create a feature or defect).
Electron beam inspection systems, for example, typically comprise an electron beam column and a stage to hold and transport the wafer being inspected. The electron beam column generally comprises an electron source, which emits electrons that are collimated and accelerated along the central axis of the column, and an electron-optical column, which consists of one or more electrostatic deflectors as well as one or more focusing lenses that aim the beam at the targeted area on the substrate.
A stage can be positioned using precise location information obtained using, for example, laser interferometry.
Generally, wafer inspection using a charged particle beam is performed by raster scanning the beam across the wafer surface. In raster scanning, the charged particle beam is deflected repetitively back and forth over the wafer, and is incrementally moved—by deflection, movement of the stage, or both—in a roughly orthogonal direction relative to the wafer as each long stripe is completed (i.e., moving much like the electron gun raster scan used to generate a typical cathode ray tube television image).
Vector scanning is another known method of moving a charged particle beam across a wafer surface. In vector scanning, the charged particle beam is deflected, sequentially, directly to the features to be inspected.
Defect recognition is typically achieved by “die-to-die” data comparison, or image-to-design comparison. Generally, wafers are removed from vacuum following electron beam lithography and transferred to a defect inspection system for the purpose of inspection and review of defects.
Single beam and multiple beam charged particle beam inspection systems have also been proposed. For example, single column and multiple column electron beam designs, in which a column emits a single electron beam, include multiple physically separate electron beam columns clustered together.
One use for charged particle beams is electron beam lithography, in which electron beams pattern features at high resolution.